Palette quantization notes: reducing colors without making an image muddy

I’ve been thinking about a small image-processing problem lately: how to reduce an image to a limited palette without making it look muddy. This comes up in a lot of places: pixel art tools printable pattern generators low-color previews LED matrix displays icons and small thumbnails craft or grid-based workflows The easy version is: pick the nearest color for every pixel. The hard version is: keep the important shapes readable after the palette gets much smaller. Nearest color is only the baseline A simple nearest-color pass usually works like this: Take each pixel. Compare it with every color in the target palette. Pick the closest one. Replace the pixel. That gives you a valid output, but not always a good one. The problem is that closest is local. It does not know whether the whole image still reads well. A face can lose warm midtones. A shadow can turn into a flat dark blob. A small highlight can disappear. Skin, fur, fabric, and background colors can collapse into the same bucket. So palette reduction is not just a color problem. It is also a structure problem. RGB distance can be misleading A common first attempt is Euclidean distance in RGB: function rgbDistance(a, b) { return Math.sqrt( (a.r - b.r) ** 2 + (a.g - b.g) ** 2 + (a.b - b.b) ** 2 ); } This is easy to implement, but it does not match human perception very well. Two colors can be numerically close in RGB and still feel different. Other colors can be farther apart numerically but visually acceptable. A better approach is to compare colors in a more perceptual color space, such as Lab or OKLab. You still have to be careful, but the distance metric starts closer to what the eye notices. Dithering helps, but it changes the style Error diffusion, like Floyd-Steinberg dithering, can preserve gradients and perceived detail with fewer colors. That is useful when the output is meant to look like a low-color image. But dithering is not always desirable. In grid-based outputs, it can create scattered single-p